Reflection Symmetry in Triangles

In this activity we are going to look at the reflection symmetry of triangles.How many lines of symmetry does an equilateral triangle have?The red triangle has been reflected in the black line to create the blue triangle.By moving the orange points, place the line in one of the mirror lines of the red triangle.If it is indeed a mirror line, then the blue triangle will sit exactly on the red triangle. Why is this the case?How many lines of symmetry could you find this way? Does this match your previous answer?

Now reset the activity by pressing the button in the top right of the activity.This time, change the red equilateral triangle into a red isosceles triangle by moving the vertices (corners).How many lines of symmetry does this triangle have?Check by moving the line as above.

Now try the same thing with other types of triangles. Can you name all the different types of triangles you make? How many lines of symmetry does each have?

Ideas for TeachersThis activity is designed for the pupils to use, so ideally they will have access to a computer to explore the ideas. The added element of making all the triangles tests their knowledge in this area too. You might want them to explain all the symmetries of one type of triangle in groups after the exploration.

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